Insulin resistance is a marker for increased risk of Non-Insulin-Dependent Diabetes Mellitus (NIDDM), Gestational Diabetes Mellitus (GDM), hypertensio and cardiovascular disease, and is a major cause of glucose intolerance in NIDD GDM, and obesity. The overall goal in this study is to define the heritabi ty of insulin resistance by studying monozygotic and dizygotic twins.